Add support for React 16

[joshwcomeau]

With React's official launch, I figured it was time to update the peer dependencies!

While trying to publish, I ran into some trouble; it wasn't able to find babel-cli when running the lib build step :/

Upgrading the dependency seems to fix it (publish still failed, but only because I hadn't yet incremented the version). I figured before I published, though, I should get another pair of eyes.

Mainly I'm curious if there's a more-ideal way to add support for React 16 in the peer dependencies.

[joshwcomeau]

Guess I never pushed the 2.9.15 branch, my bad. That was the release for zombie-nodes bugfix.

[Hypnosphi]

Did you test it with components returning strings or fragments?

[Hypnosphi]

a more-ideal way to add support for React 16 in the peer dependencies

How about wildcard?

[tobilen]

i'll spend most of tomorrow upgrading our codebase to react16. i'd like to give feedback after that.
my gut feeling though, some simple fail-safes should be implemented to raise/throw when fragments are being passed to flip-move.

something along the lines of ```js
if (typeof this.props.children === 'string' || typeof this.props.children === 'array') console.warn('react-flip-move doesnt support arrays or strings as components yet.');

[tobilen]

would "react": ">=0.13.x <=16.x.x", work?

[Hypnosphi]

if (typeof this.props.children === 'string' || typeof this.props.children === 'array')

It should be not about this.props.children, but rather about output of each child's render.

[tobilen]

check is not needed anymore when we merge #191

[joshwcomeau]

This is no longer needed thanks to @tobilen's fantastic work :D